I use a large enough deep wall socket over the lead end and a large flat washer on the bulb end in a bench vice. The bulb socket will slide into the deep wall socket when you tighten the vice on the washer end. The metal parts of the lamp assembly, including the lens retaining screw, should be gold zinc plated. In reality the rivets should be drilled out before plating and new ones installed after, but that gets to be expensive as you need a rivet tool, dies and the correct size rivets are about $19.00 a bag of 100. To do it "correct", NPD sell a black insulating sleeve that can be used to replace the old one. The NPD sleeve will do three lamps, it's a bit long. You will need to carefully remove the contact at the bulb end of the socket, disassemble the socket, replace the sleeve, re-assemble the socket and solder the contact back in place. Clean as you go. The critical item is the grommet on the wire that goes thru the rear panel. Be careful with that. To re-install the bulb socket, reverse the procedure with the bench vice with an additional deep wall. I made a "tool" from a 3 inch long piece of 3/4 inch electrical conduit to help. If the bulb socket slides in (or out) too easily, "deform" the hole slightly and try again. New foam weather strip to seal the glass is available at NPD as well.
Jim